Magnesium Sulfate Attenuate Opioid Tolerance in Patients undergoing Major Abdominal Surgery

BACKGROUND: Magnesium is a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor. Magnesium is thought to be involved in opioid tolerance by way of inhibiting calcium entry into cells. METHODS: The patients were randomly assigned to three groups according to the anesthetic regimens: Group M received magnesium sulfate and Group C received saline intravenously under remifentanil-based anesthesia. Group S received saline intravenously under sevoflurane based anesthesia in place of remifentanil. The patients in the group M received 25% magnesium sulfate 50 mg/kg in 100 ml of saline, and those patients in groups C and S received an equal volume of saline before induction of anesthesia; this was followed by 10 mg/kg/h infusion of either magnesium sulfate (group M) or an equal volume of saline (groups C and S) until the end of surgery. Pain was assessed on a visual analog scale at 1, 6, 12, 24, and 36 hours after the operation. The time to the first postoperative analgesic requirement and the cumulative analgesic consumption were evaluated in the three groups. RESULTS: The visual analog scales for pain and the cumulative analgesic consumption were significantly greater in group C than in other groups. The time to first postoperative analgesic requirement was significantly shorter in group C than that in the other groups. There were no differences between group M and S for side effects. CONCLUSIONS: A relatively high dose and continuous remifentanil infusion is associated with clinically relevant evidence of acute opioid tolerance. NMDA-receptor antagonist, magnesium sulfate as an adjuvant analgesic prevents opioid tolerance in patients who are undergoing major abdominal surgery under high dose and continuous remifentanil infusion-based anesthesia.

The effect of magnesium sulfate on postoperative pain in patients undergoing major abdominal surgery under remifentanil-based anesthesia / 대한마취과학회지

BACKGROUND: Opioid tolerance may involve activation of the N-methyl-D-aspartate (NMDA) system. The possible involvement of the NMDA system suggests that one of the NMDA receptor antagonists, magnesium may be a useful adjunct to opioids for the treatment of postoperative pain following remifentanil infusion. METHODS: For this study, 70 patients scheduled for major abdominal surgery under remifentanil-based anesthesia were randomly allocated into groups that received either magnesium sulfate (group M) or saline (group C) intravenously. The patients in the group M received 25% magnesium sulfate at a dose of 50 mg/kg in 100 ml of saline, and those in the group C received an equal volume of saline prior to the induction of anesthesia. In addition, patients in both groups received 10 mg/kg/h infusion of either magnesium sulfate (group M) or an equal volume of saline (group C) until the end of surgery. Pain was assessed using a visual analog scale at 30 min, and 6, 12, 24, and 36 hours after operation. The time to the first use of postoperative analgesic and cumulative analgesic consumption in both groups were also evaluated. RESULTS: The visual analog scale scores for pain and cumulative analgesic consumption were significantly lower in the group M than in the group C. The time to the first use of postoperative analgesic was significantly shorter in group C than in the group M. CONCLUSIONS: Use of the NMDA-receptor antagonist, magnesium sulfate as an adjuvant analgesic reduced postoperative pain in patients undergoing major abdominal surgery under remifentanil-based anesthesia.